475
CEMENT.
SIEVES.
Description.	Meshes.			
	Number of.	Per square	Size.	
		inch.	Maximum. Minimum.	
	«40 «60 «80 «100 98 x 100 112 x 118 155 x 170 188 x 198 174 x 182	« 1,600 «8,600 «6,400 10,000 » ׳ 9,800 13,216 26,350 37,224 31,668	Inch. .0162 .0148 .0090 .0079 .0058 .0051 .0037 .0031 .0027 b .0020	Inch. .0132 .0078 .0057 .0056 0057 .0050 .0034 .0028 .0025
				
				
				
				
« Nominal.	b About.
The 188 x 198 brass wire cloth and the No. 20 bolting cloth were each commercially rated as No. 200 sieves. The openings in the bolting cloth were smaller than those of the wire sieve, notwithstanding the lesser number of meshes per.square inch, due to the difference in the diameter of the wire and the size of the silk threads, modified by the manner in which the bolting cloth is woven to maintain meshes of uniform size throughout the fabric. In order to obtain a finer sieve a brass wire cloth was electroplated, increasing the size of the wires and diminishing the openings. In this manner meshes were obtained which measured about ".002 and less in diameter. It was very slow work using the plated sieve and the practical limit of fineness is found in the No. 20 bolting cloth. Finer material was separated by the use of a winnowing device in which an air blast was directed against the cement as it fell from the No. 20 bolting cloth, collecting the material which settled in a trough at different distances from the sieve. The sieve was attached to a clapper which was adjusted in front of a toothed wheel, and upon rotating the latter a very energetic shaking took place. The approximate sizes of the coarser grains thus sorted, measured by means of a microscope, using polished sections of tensile briquettes, are given below:
Grade.	Diameter of grains.	
	Maximum.	Average.
0		Inch. .0025 . 0021 .0017 .0013 .0008	Inch. .0013 .0010 .0008 .0004 . 0002
		
B			
		
E			
		
Finer grains were carried down with the coarser parts in each grade, measuring ".0001 and less in diameter. The largest part of the winnowed material was collected in grades O, I A, and A, which comprised 90 per cent of that which passed through the sieve, 6 per cent was in grade B, less than 2 per cent in grade 0, and less than 1 per cent each in D and E. The separation into different sized grains was generally